Going for it: Kai, 8 - who is a regular guest on the popular talk show - wholeheartedly sang along to the Sheeran classic, Thinking Out Loud

Unaware: Little did he know that his idol Ed came out mid-way through his performance and plonked himself on the sofa behind him

'Aw that's beautiful!': Ellen applauded Kai before gesturing him to look behind where he was met by Ed

'I was literally watching you in the dressing room!' Ed told Kai, who by this time could only muster up the word 'hi' again.

Meanwhile, Ed proved he hadn't lost his sense of humour as he poked fun at his chubbier self last year, during his interview on the long-running chat show.

'God, I was a bit fat then? Jesus!' the talented star exclaimed in mock-horror while surveying a photo of himself at the Grammys last year.

'Wow!' he deadpanned humorously as he looked at the photo of him in a black suit on the screen

His revelation came as he discussed being able to relax at the Grammys this year as he wasn't up for any awards.

'There was no pressure,' he explained. 'I only went out in the audience for the Bieber song that I helped write [Love Yourself] and then the rest of the time I spent with my family backstage so it was pretty fun.'

Star struck: Kai could only muster up the word 'hi' again

Humble: Meanwhile, Ed proved he hadn't lost his sense of humour as he poked fun at his chubbier self last year, during his interview on the long-running chat show

Self-deprecating: 'God, I was a bit fat then? Jesus!' the 25-year-old singer exclaimed in mock-horror to while surveying a photo of himself at the Grammys last year

Transformation: He has shed a whooping 3.5 stone since last year's Grammys (left) and this year's (right)

Ed previously admitted his hockey player girlfriend Cherry Seaborn had helped him slim down after he ballooned to 15st whilst indulging on pizza and beer during his year off from touring.

Speaking with Total Access on Signal 1 radio, he said: 'I didn’t realise how active I was on tour. My diet was pizza and beer, but because I was doing two hours a night I was really in shape.

'I stopped touring and carried on my diet of pizza and beer. Suddenly I didn’t fit in anything. I was like, "All my clothes have shrunk."'

Of the new workout regime that got him back into shape, he revealed: 'I did 10 minutes a day without fail – intervals of 30 seconds sprinting and 30 jogging.

'The key is to not miss a day, so you don’t have to do an hour.'

Meanwhile, later in his chat with host Ellen, Ed revealed he had binned his phone in a bid to get rid of the stress in is life.

Tough: Of the new workout regime that got him back into shape, he revealed: 'I did 10 minutes a day without fail – intervals of 30 seconds sprinting and 30 jogging'

Ouch! He also revealed that he scalded the skin off his foot after accidentally stepping in an active volcano in Iceland

'I got rid of my phone as my New Year's resolution. I still don't have it. I bought an iPad and I just work off emailing and it's so much less stress.

'I don't wake up in the morning and have to answer 50 messages of people asking for stuff - I just wake up and have a cup of tea,' he quipped chuckling.

The Thinking Out Loud star also recounted a wince-inducing tale in which he scalded the skin off his foot after accidentally stepping in an active volcano in Iceland.

'I have a lot of accidents because I'm a bit of a clumsy idiot,' he began self-deprecatingly. We were up the top of an active volcano, bubbling and boiling - it's called a geyser - it's like a pool of more than boiling water basically.

New Year's resolution: Ed added that he no longer used his phone and only worked with emails on his iPad to help cut out the stress in his life

'I was like "Oh, that looks cool!" and they were like "No, don't look over there!" and my foot slipped in. I've never had the feeling of dying before but it fell in and it all went in slow motion, I was like "Right, well, that's it!' he recalled.

He added that because of the pain he peeled his sock off - and accidentally took off a layer of scalded skin too as a result - to cries of horror from the audience.

Ed has returned after taking a year out from music to go travelling and 'see a country for what it is'.

'I went travelling for a year. I come from the countryside in England and it's such a beautiful place and I always get really annoyed when everyone from all over the world are like "London was amazing" but haven't seen anywhere else.

'I found that I'd done that in every country I'd ever been to, like I'd gone to Japan and been like "Tokyo's amazing!", he admitted.

'So being able to travel and actually go to the cities was my goal for last year and actually see a country for what it is rather than just the capital.'

Proud: 'I don't wake up in the morning and have to answer 50 messages of people asking for stuff - I just wake up and have a cup of tea,' he quipped chuckling